Vertebrate corneas become transparent by a mechanism which remains unelucidated. Transparency does not arise coincident with the beginning of keratan sulfate biosynthesis, as was once thought. However, the apparent degree of sulfation of keratan sulfate and other glycosaminoglycans increases as transparency appears. Nevertheless, the specific activities of glycosaminoglycan sulfotransferases in the cornea remain reasonably constant during development. Thus, if the degree of sulfation of glycosaminoglycans controls corneal transparency to some degree, it may be regulated by the availability of the sulfate donor (PAPS), by extracellular sulfotransferases, or by both. Proposed research will test these hypotheses. Using a combination of immunological and biochemical techniques, as well as GLC/mass spectroscopy and ion-selective microelectrodes, we propose to study: 1) differentiation of corneal fibroblasts from the neural crest and their relation to other fibroblast populations in the eye (e.g., in limbus); 2) control of glycosaminoglycan and glycoprotein biosynthesis in the developing cornea, including the role of such extracellular enzymes as sulfotransferases; 3) regulation of collagen biosynthesis by corneal cell-types, including the mechanism by which orthogonal gridworks of collagen fibrils form; 4) role of the extracellular matrix in the development and maintenance of corneal transparency, including ultrastructural localization of the core proteins of proteoglycans and hormonal control of ionic activities in the stroma; and 5) role of extracellular materials in controlling the invasiveness of presumptive corneal fibroblasts and corneal nerves.